Until I, a supporting character, become the heroine

High schooler Rui wakes up in a mysterious dungeon, where she meets Claude who saves her from a monster. She realizes that she has been transported to another world, the world of the popular otome game "Tower of God," along with another transmigrator, Mayu, who has a mark proving that she is the heroine. However, Rui has no mark and cannot use magic. In order to return to her original world, mob Rui follows Mayu d...